Wednesday, March 26, 2014

Influence of biochar in seed germination and growth rate (part 1)

Biochars affects seed germination and fast growth of seedlings
     Biochar has been reported to both increase (Chan et al. 2008; Yamato et al. 2006) and decrease (Deenik et al. 2010) plant growth and yield but there have been few studies reporting the influence of biochar on early stages of plant growth such as on seed germination and seedling growth. The stimulation or inhibition of seed germination due to biochar application has mostly been investigated for forest plants (Choi et al. 2009; Pierce and Moll 1994; Reyes and Casal 2006; Tian et al. 2007).

    For agricultural plants,activated charcoal (steam treated) enhanced seed germination of potato (Bamberg et al. 1986) while Van Zwieten et al. (2010) showed that wheat seed germination was increased with a single dose (10 t/ha) of paper mill biochar. In contrast, Free et al. (2010) reported that maize seed germination and early growth were not significantly affected by biochars made from a range of organic sources.

       The application of biochar to soil can alter organic matter mineralization (Steiner et al. 2008; Wardle et al. 1998) which is linked to the release of nutrients such as nitrogen (Manzoni et al. 2008; Murphy et al. 2003). The resultant change in nutrient status of the soil may affect both seed germination and seedling growth.

     Application of biochar to acidic soils can increase soil pH to alkaline levels, especially if higher rates of biochar are applied and changes occur to soil cation exchange capacity (CEC) (Ogawa 1994). The diversity in characteristics of biochar indicate that biochar responses will depend on the type and rate of biochar applied to soil as well as on soil characteristics such as soil C, pH, CEC and other components of soil fertility.

pH and EC
The pH and EC of biochar were measured in water at 1: 5 (w/v) ratios. Soil pH was also measured in CaCl2 at 1:5 (w/v) ratios. 

Soil-less Petri dish bioassay 
     15 (zea maiz) seeds were sown in Petri dishes (8.5 cm diameter) on a layer of filter paper moistened with deionized water.  20 mL of DI water was added to the Petri dish for each rate of biochar. Each of the four biochar types was added at the rates 0, 0.5, 1.0, 2.5, 5.0 g/Petri dish (equivalent to 0, 10, 20, 50, 100 t/ha on a volume basis at 10 cm soil depth) with three replicates following the design recommended by Morrison and Morris (2000) where an individual Petri dish was considered as a replicate and a control treatment was used for each biochar.

Rates of biochar to be applied in germinations
     All Petri dishes were covered with lids and incubated in the dark at 25°C for 72 h after germination percentage and root length was assessed. Root length of germinated seeds was measured in fresh roots using a ruler, and summed for each Petri dish (m/Petri dish). 

Preparation of germination in petri dish

     Effect of biochar at different rates 0, 0.5, 1.0, 2.5, 5.0 g/Petri dish (equivalent to 0, 10, 20, 50, 100 t/ha based on10 cm field depth) on seed germination average conducted in the soil less Petri dish bioassay.

Petri dish bio-assay

Coconut fiber

Palm fiber

Criptomeria japonica

    Most of the biochars used in these experiments were alkaline (pH in water 8.1 to 9.11). TDS: for ppt, ppm and EC, coconut fiber biochar showed the highest contents. Being eucalyptus biochar the one with the lowest levels.

Growth rate
     Biochar type and application rate influenced wheat seed germination and seedling growth in the soil-less Petri dish and soil-based bioassay. Germination in coconut fiber, eucalyptus and palm fiber showed little difference among them, being criptomeia japonica the biochar with less seeds germinated.

     Fig 1). Early root growth of corn seeds was different in response in eucalyptus biochar compared to the results of the other three biochars (figures 2,3,4 and 5).

Germination average (Figure 1)

Palm fiber (Figure 2)

Coconut fiber (Figure 3)

Eucaliptus   (Figure 4)

Criptomeria japonica (Figure 5)

ICP of biochars (Figure 6)

     In conclusion, the four biochar types used in this study generally increased wheat seed germination at rates of application <10 and <50 t/ha the rest of the treatments tended to inhibit germination at the highest rate of application under the bioassay conditions.

    This investigation supports the proposal of Major (2009) that a germination test could be a useful screening process for evaluating biochars. However, it is important to use several rates of biochar in the bioassay because of differences in response observed in this study. ICP analyses (fig.6) determined the contents of various elements in the biochars showing similarities in Fe, Pb, Zn, Cr, Na, and Cu, with differences in K, Ca, and Mg.

    We recommend the soil-less Petri dish bioassay as a preliminary ecotoxicological test for biochar screening because it is rapid and simple, and it avoids the need for use of a ‘standard’ soil which is difficult to collect, transport and maintain across quarantine boundaries. Finally, it is recommended that toxicity bioassays for biochar are repeated (in addition to the replication used within each test) to ensure reproducibility.

Table with all the information showed in graphs


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